Method of forming a flexible semiconductor layer and devices on a flexible carrier

ABSTRACT

A method for fabricating a semiconductor device comprises providing a preformed spalled structure comprising a stressor layer stack on a first surface of a semiconductor substrate; forming an interfacial release layer on an exposed second surface of the semiconductor substrate; adhesively bonding the interfacial release layer to a rigid handle substrate using an epoxy; removing at least a portion of the stressor layer stack from the first surface of the semiconductor substrate; processing the semiconductor substrate; and removing the semiconductor substrate from the interfacial release layer to impart flexibility to the semiconductor substrate.

CROSS REFERENCE

This patent application is a divisional application of U.S. patentapplication Ser. No. 14/795,019, filed Jul. 9, 2015, the disclosure ofwhich is incorporated by reference herein in its entirety.

BACKGROUND

The exemplary embodiments described herein relate generally tosemiconductor devices and methods for the fabrication thereof and, morespecifically, to methods of using an interfacial release layer totemporarily bond a flexible semiconductor layer to a substrate for thesubsequent transfer of the flexible semiconductor layer to a flexiblecarrier.

Flexible semiconductor layers produced by spalling techniques (describedin U.S. Patent Application Publication No. 2010/0311250 A1 to Bedell etal.) can be difficult to process. Such techniques generally employ thetemporary bonding of a flexible semiconductor layer to a handlesubstrate and subsequent separation of the flexible semiconductor layerfrom the handle substrate. The temporary bonding is often incompatiblewith various processing parameters. For example, processing of thesemiconductor layer/handle substrate assembly may occur at temperaturesas high as 180 degrees C. to 250 degrees C. After processing at suchtemperatures, separation of the semiconductor layer from the handlesubstrate without causing damage to the semiconductor layer may bedifficult.

The difficulty in separation of the semiconductor layer from the handlesubstrate is generally the result of the temporary bonding utilizingeasy-release tapes that are either not stable at the processingtemperatures required or which lose their easy-release properties afterbeing exposed to such temperatures. In addition, air bubbles at thetape/semiconductor layer interface are easy to form yet difficult toremove, the difficulty in removing such bubbles resulting from the tapenot being be easily peeled from the semiconductor layer and repositionedwithout incurring damage.

Difficulty in separation of the semiconductor layer from the handlesubstrate may also be the result of approaches that utilize epoxies tobond the various layers of the devices. The use of epoxies may appear tobe more forgiving than those that employ tapes since (unlike tapes)interfacial air bubbles may be kneaded out of the epoxy before settingoccurs. Many epoxies also have the advantage of being stable to thetemperatures at which processing occurs. However, adhesive bonds withepoxies are generally permanent, which thereby inhibits clean separationof the semiconductor layer from the handle substrate.

BRIEF SUMMARY

In one exemplary aspect, a method for fabricating a semiconductor devicecomprises providing a preformed spalled structure comprising a stressorlayer stack on a first surface of a semiconductor substrate; forming aninterfacial release layer on an exposed second surface of thesemiconductor substrate; adhesively bonding the interfacial releaselayer to a rigid handle substrate using an epoxy; removing at least aportion of the stressor layer stack from the first surface of thesemiconductor substrate; processing the semiconductor substrate; andremoving the semiconductor substrate from the interfacial release layerto impart flexibility to the semiconductor substrate.

In another exemplary aspect, a method for fabricating a semiconductordevice comprises providing a preformed spalled structure comprising astressor layer stack on a first surface of a semiconductor substrate;forming an interfacial release layer on a second exposed surface of thesemiconductor substrate; bonding the interfacial release layer to arigid handle substrate using an epoxy adhesive; removing at least aportion of the stressor layer stack from the semiconductor substrate;processing the semiconductor substrate; applying a back contact layer tothe semiconductor layer; isolating cells in the back contact layer inthe semiconductor substrate; and removing the semiconductor substratefrom the interfacial release layer using a pressure-sensitive carriertape to impart flexibility to the semiconductor substrate.

In another exemplary aspect, a method for fabricating a semiconductordevice comprises providing a preformed spalled structure comprising astressor layer stack on a first surface of a semiconductor substrate;forming an interfacial release layer on a second exposed surface of thesemiconductor substrate; bonding the interfacial release layer to arigid handle substrate using an epoxy adhesive; removing at least aportion of the stressor layer stack from the semiconductor substrate;processing the semiconductor substrate; forming a layer comprising afinger/bus metal and an anti-reflective coating on the semiconductorsubstrate; applying a sacrificial mask to the layer comprising thefinger/bus metal and the anti-reflective coating; patterning the layercomprising the finger/bus metal and the anti-reflective coating;removing the sacrificial mask; and removing the semiconductor substratefrom the interfacial release layer using a tape superstrate to impartflexibility to the semiconductor substrate.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing and other aspects of exemplary embodiments are made moreevident in the following Detailed Description, when read in conjunctionwith the attached Drawing Figures, wherein:

FIGS. 1A through 1D are schematic representations of exemplary methodsof temporarily bonding a flexible semiconductor device to a flexiblecarrier;

FIGS. 2A through 2D are schematic representations of exemplary methodsof temporarily bonding a flexible semiconductor device to a flexiblecarrier using a release layer;

FIG. 2E is a schematic representation of using pressure-sensitivecarrier tape to remove the flexible semiconductor device from therelease layer;

FIGS. 3A through 3E are schematic representations of exemplary methodsof temporarily bonding a flexible semiconductor device to a rigid handlesubstrate using a release layer;

FIGS. 3F and 3G are schematic representations of forming and isolatingcells in the flexible semiconductor device of FIGS. 3A through 3E usinga blanket layer of hardmask;

FIG. 3H is a schematic representation of using pressure-sensitivecarrier tape to remove the flexible semiconductor device and a layer ofhardmask from the release layer;

FIGS. 3I and 3J are schematic representations of usingpressure-sensitive carrier tape to remove the flexible semiconductordevice from the release layer;

FIGS. 4A through 4E are schematic representations of exemplary methodsof temporarily bonding a flexible semiconductor device to a rigid handlesubstrate using a release layer;

FIG. 4F is a schematic representation of depositing a back surface fieldlayer on the flexible semiconductor device of FIGS. 4A through 4E;

FIGS. 4G and 4H are schematic representations of forming and isolatingcells in the flexible semiconductor device of FIGS. 4A through 4F usinga blanket layer of hardmask;

FIG. 4I is a schematic representation of using pressure-sensitivecarrier tape to remove the flexible semiconductor device from therelease layer;

FIGS. 5A through 5E are schematic representations of exemplary methodsof forming and temporarily bonding a flexible semiconductor device to arigid handle substrate using a release layer;

FIGS. 5F through 5I are schematic representations of depositing afinger/bus and sacrificial mask on the flexible semiconductor device ofFIGS. 5A through 5E;

FIGS. 5J and 5K are schematic representations of disposing a tapesuperstrate on the flexible semiconductor device of FIGS. 5A through 5Ito remove the flexible semiconductor device from the release layer;

FIG. 5L is a schematic representation of a contact on the flexiblesemiconductor device of FIGS. 5A through 5K after removing thesuperstrate;

FIG. 6 is a simplified block diagram of exemplary electronic devicesthat are suitable for use in the fabrication of flexible semiconductorlayers and devices on flexible carriers;

FIG. 7 is a logic flow diagram that illustrates the operation of anexemplary method, and a result of execution of computer programinstructions embodied on a computer readable memory, in accordance withan exemplary embodiment of the fabrication of flexible semiconductorlayers and devices on flexible carriers; and

FIGS. 8A through 8D are photographs of the silicon film transfer ofFIGS. 2C through 2E at various stages.

DETAILED DESCRIPTION

Exemplary embodiments of methods for forming flexible semiconductorlayers and devices on flexible carriers and structures associatedtherewith are disclosed herein. Such methods and structures include, butare not limited to, the use of temporary bonding layers comprisingepoxies in conjunction with release layers and spalling techniques.However, it should be understood that the disclosed embodiments aremerely illustrative of the claimed methods and structures and that suchmethods and structures may be embodied in various forms. The methods andstructures disclosed herein may be embodied in many different forms andshould not be construed as limited to the exemplary embodiments setforth herein.

The spalling techniques used to form the flexible semiconductor layerson the flexible carriers allow for controlled removal of relatively thinlayers of semiconductor materials forming the semiconductor layers fromrigid handle substrates to which the semiconductor layers aretransferred.

Referring to FIGS. 1A through 1D, one exemplary method of forming aflexible semiconductor layer on a flexible carrier is shown generally at100 and is hereinafter referred to as “method 100.” As shown in FIG. 1A,a preformed spalled structure is provided, the structure comprising aspall-inducing stressor layer stack 110 (comprising at least, forexample, an adhesion layer 115, a seed/stressor layer 120, and atransfer tape 125) attached to a flexible semiconductor material 130,which is made to contact an epoxy adhesive 135 disposed on a rigidhandle substrate 140 such that the flexible semiconductor material 130interfacially engages the epoxy adhesive 135.

As shown in FIG. 1B, pressure is applied to one or both of the stressorlayer stack 110 and the rigid handle substrate 140 such that the epoxyadhesive 135 is substantially uniformly distributed on the rigid handlesubstrate 140. The epoxy adhesive is then typically cured at atemperature of from about 40° C. to 150° C. for a period of time betweenabout 0.1 hours to about 5 hours. The transfer tape 125 is removed fromthe stressor layer stack 110 after the curing step.

As shown in FIG. 1C, the adhesion layer 115 and the seed/stressor layer120 are removed from the flexible semiconductor material 130, and atthis point the flexible semiconductor material 130 has been transferredto the rigid handle substrate 140.

As shown in FIG. 1D, a peel tape (pressure-sensitive carrier tape 160)is applied to the flexible semiconductor material 130 and is used toremove the flexible semiconductor material 130 from the epoxy adhesive135. As shown, removing the flexible semiconductor material 130 usingthis technique may result in a less than desirable transfer of theflexible semiconductor material 130, such as an incomplete separation ofthe flexible semiconductor material 130 from the epoxy adhesive 135 or adisintegration of the flexible semiconductor material 130 and/or epoxyadhesive 135.

Referring now to FIGS. 2A through 2E, one exemplary method of using aninterfacial release layer in forming a flexible semiconductor layer on aflexible carrier is shown generally at 200 and is hereinafter referredto as “method 200.” Method 200 allows for the temporary bonding of thesemiconductor layer to a rigid or semi-rigid substrate coated with anepoxy adhesive followed by the transfer of the flexible semiconductorlayer to the flexible carrier.

As shown in FIG. 2A, the epoxy adhesive (shown at 235) is disposed on ahandle substrate 240. The epoxy adhesive 235 may comprise anelectrically conductive epoxy comprising silver. The handle substrate240 may be rigid or semi-rigid and has a front surface 242 (at least aportion of which receives the epoxy adhesive 235) and a back surface244. In exemplary embodiments in which the handle substrate 240 isrigid, materials from which the handle substrate 240 may be formedinclude, but are not limited to, Si, Ge, quartz, borosilicate glass,sapphire, metals, ceramics, combinations of the foregoing materials, andthe like.

Still referring to FIG. 2A, a preformed spalled structure is providedcomprising a spall-inducing stressor layer stack 210 that is attached toa semiconductor layer 230. The stressor layer stack 210 may comprise anadhesion layer 215 of titanium (deposited on the semiconductor layer230), a seed layer 216 of nickel on the adhesion layer 215, a stressorlayer 220 of nickel deposited onto the seed layer, and an ultraviolet(UV) releasable tape 225 applied to the stressor layer 220. Thesemiconductor layer 230 (e.g., a 100-oriented silicon material forming asubstrate or any material selected from the group consisting of silicon,germanium, SiGe, bulk III-V materials, any of the foregoing materialsfurther including epitaxially grown semiconductor layers, any of theforegoing materials further including doped layers, metallic layers,and/or passivating layers, and combinations of the foregoing) has anexposed front surface and a back surface to which the stressor layerstack 210 is attached. A contact-hole patterned passivation layer mayalso be deposited on the semiconductor layer 230, with a blanketconductive layer in contact with the passivation layer and thesemiconductor layer 230 exposed by the contact-holes. Methods by whichthe adhesion layer 215 is deposited on the seed layer and the seed layeris deposited on the adhesion layer 215 include, but are not limited to,thermal evaporation, or sputtering.

As shown in FIG. 2B, an interfacial release layer (shown at 250) isformed on an exposed surface of the semiconductor layer 230 prior tobonding of the semiconductor layer 230 with the interfacial releaselayer 250 to the epoxy adhesive 235 on the handle substrate 240. Whenthe semiconductor layer 230 comprises a silicon or siliconoxide-containing semiconductor material, the interfacial release layer250 comprises aluminum. However, while aluminum on a native siliconoxide-containing semiconductor material provides a suitable interfacialrelease layer 250, other materials (alone or in combination withaluminum) may be used as well. For example, carbon or hydrocarboncontamination may be introduced to the silicon surface prior to thealuminum deposition. Suitable methods for depositing the aluminuminterfacial release layer 250 onto the semiconductor layer 230 include,but are not limited to, thermal evaporation, or sputtering.

As shown in FIG. 2C, the interfacial release layer 250, along with theattached semiconductor layer 230, is transferred and bonded to the epoxyadhesive 235 on the handle substrate 240 using pressure to substantiallyuniformly distribute the epoxy adhesive on at least a portion of thefront surface 242 of the handle substrate 240, thereby facilitating asubstantially bubble-free epoxy adhesive bond between the handlesubstrate 240 and the semiconductor layer 230. The epoxy adhesive isthen typically cured at a temperature of from about ° C. to about 150°C. for a period of time between about 0.1 hours to about 5 hours. The UVreleasable tape 225 is removed from the stressor layer 220.

As shown in FIG. 2D, some or all of the stressor layer stack 210 isremoved from the semiconductor layer 230 (for example, by an etchingprocess or an acid wash). Processing steps (e.g., patterning, thermaltreatments (such as heating, if necessary), film depositions, and thelike) are then performed on the semiconductor layer 230 as well as onany layers thereupon formed (e.g., from the patterning, filmdepositions) to form a processed semiconductor layer 230 that isflexible upon release from handle substrate 240. At least a portion ofthe processed, flexible semiconductor layer 230 desired for removal fromthe interfacial release layer 250 is identified and then contacted withthe pressure-sensitive carrier tape 260.

As shown in FIG. 2E, a tape-initiated separation process is carried outusing the pressure-sensitive carrier tape 260. In the tape-initiatedseparation process, the flexible semiconductor layer 230 is peeled awayfrom the interfacial release layer 250, leaving the interfacial releaselayer 250 on the epoxy adhesive 235 and at least a portion of theprocessed, flexible semiconductor layer 230 on the pressure-sensitivecarrier tape 260. The interfacial release layer 250 has the property ofbeing sufficiently adhesive to the flexible semiconductor layer 230 andthe epoxy adhesive 235 during the processing but is weakly adhesiveenough to allow for the separation of the flexible semiconductor layer230 from the interfacial release layer 250 after processing.

Referring now to FIGS. 3A through 5L, various exemplary methods offorming a flexible semiconductor layer on a flexible carrier layer areshown. In such exemplary methods, desired processing steps may includepatterning a semiconductor layer into separate chiplet regions, witheach chiplet region being individually attached to an underlying epoxylayer.

As shown in FIGS. 3A through 3F, one exemplary method of producing asemiconductor device is shown generally at 300 and is hereinafterreferred to as “method 300.” In method 300, processing of the flexiblesemiconductor layers is minimal. For example, in a first exemplarymethod of processing, an additional blanket layer may be includedbetween the flexible semiconductor layer and the flexible tape (FIGS. 3Gand 3H), and in a second exemplary method of processing, the flexiblesemiconductor layer may be disposed directly on the flexible tape (FIGS.3I and 3J).

As shown in FIG. 3A, a spall-inducing stressor layer stack 310 is formedand deposited onto a substrate comprising a semiconductor material(e.g., a 100-oriented silicon material forming a substrate or anymaterial selected from the group consisting of silicon, germanium, SiGe,bulk III-V materials, any of the foregoing materials further includingepitaxially grown semiconductor layers, any of the foregoing materialsfurther including doped layers, metallic layers, and/or passivatinglayers, and combinations of the foregoing) configured to form aminimally processed flexible semiconductor layer 330. The stressor layerstack 310 comprises an adhesion layer 315 of titanium deposited on thesemiconductor material forming the semiconductor layer 330 as well as aseed layer 316 of nickel deposited on the adhesion layer 315. Acontact-hole patterned passivation layer may also be deposited on thesemiconductor layer 330, with a blanket conductive layer in contact withthe passivation layer and the semiconductor layer 330 exposed by thecontact-holes. Methods by which the adhesion layer 315 is deposited onthe semiconductor layer and the seed layer is deposited on the adhesionlayer 315 include, but are not limited to, thermal evaporation orsputtering. A stressor layer 320 of nickel may be deposited onto theseed layer. An ultraviolet (UV) releasable tape 325 may then be appliedto the stressor layer 320.

The process of controlled spalling separates semiconductor material 330at a plane 333 extending longitudinally through the semiconductormaterial 330 parallel to the adhesion layer 315. Separation of thesemiconductor material 330 may be facilitated by mechanically guidingthe ultraviolet (UV) releasable transfer tape 325 to induce and sustainspalling mode fracture. Separation along plane 333 results in thesemiconductor material 330 having reduced thickness T as shown in FIG.3B making the thinner semiconductor material 330 have increasedflexibility. The lower portion of the semiconductor material 330 may bediscarded or recycled.

As shown in FIG. 3C, an interfacial release layer 350 is formed on anexposed surface of the semiconductor layer 330 prior to bonding of thestressor layer stack 310 and the semiconductor layer 330 to epoxyadhesive 335 on a handle substrate 340. When the semiconductor layer 330comprises a silicon or silicon oxide-containing semiconductor material,the interfacial release layer 350 comprises aluminum. However, whilealuminum on a native silicon oxide-containing semiconductor materialprovides a suitable interfacial release layer 350, other materials(alone or in combination with aluminum) may be used as well. Forexample, carbon or hydrocarbon contamination may be introduced to thesilicon surface prior to the aluminum deposition. Suitable methods fordepositing the aluminum interfacial release layer 350 onto thesemiconductor layer 330 include, but are not limited to, thermalevaporation or sputtering.

As shown in FIG. 3D, the interfacial release layer 350, along with theattached semiconductor layer 330, is transferred and bonded to the epoxyadhesive 335 on the handle substrate 340 using pressure to substantiallyuniformly distribute the epoxy adhesive 335 on at least a portion of afront surface 342 of the handle substrate 340, thereby facilitating asubstantially bubble-free epoxy adhesive bond between the handlesubstrate 340 and the semiconductor layer 330. The epoxy adhesive isthen typically cured at a temperature of from about 40° C. to about 150°C. for a period of time between about 0.1 hours to about 5 hours. The UVreleasable tape 325 is removed from the stressor layer 320.

As shown in FIG. 3E, some or all of the stressor layer stack 310 isremoved from the semiconductor layer 330 (for example, by an etchingprocess or an acid wash). Processing steps (e.g., patterning, thermaltreatments (such as heating, if necessary), film depositions, and thelike) are then performed on the semiconductor layer 330 as well as onany layers thereupon formed (e.g., from the patterning, filmdepositions) to form a processed semiconductor layer 330 that isflexible upon release from the handle substrate 340.

Referring now to FIG. 3F, processing can be provided to include cellisolation (if desired). In one exemplary embodiment of isolating cellsin the flexible semiconductor layer 330 a hardmask 370 is deposited as ablanket layer on the flexible semiconductor layer 330 and is patternedand etched through a photoresist (PR) mask. In another exemplaryembodiment of isolating cells also using a patterned hardmask, hardmaskmaterial is deposited through a shadow mask. In either embodiment, thehardmask deposition may occur as shown and described here or prior tothe application of the stressor layer stack 310. In yet anotherexemplary embodiment of isolating cells, laser scribing of the flexiblesemiconductor layer 330 may be carried out. In any embodiment, acontiguous region of the semiconductor layer 330 may be identified, sucha region including a majority of the surface of the semiconductor layer.The processing may include the forming of a cell front structure on theregion defined by the majority of the surface.

As shown in FIG. 3G, the cells (shown at 380) are isolated from eachother by wet or dry etching and supported by the epoxy adhesive 335.

The first exemplary method of processing the cells 380 (additionalblanket layer included between the flexible semiconductor layer and theflexible tape) is illustrated in FIG. 3H. In such a method ofprocessing, the flexible pressure-sensitive carrier tape 360 is disposedon the hardmask 370 deposited as the blanket layer. The cell 380 isselectively removed from the interfacial release layer 350 by removal ofthe flexible pressure-sensitive carrier tape 360, which removes theportion of the flexible semiconductor layer 330 defining the cell 380and the hardmask 370.

The second exemplary method of processing the cells 380 (flexiblesemiconductor layer disposed directly on the flexible tape) isillustrated in FIGS. 3I and 3J. In such a method of processing, thehardmask 370 is removed (e.g., by etching), and the flexiblepressure-sensitive carrier tape 360 is disposed directly on the flexiblesemiconductor layer 330 and is used to remove the portion of theflexible semiconductor layer 330 defining the cell 380.

As shown in FIGS. 4A through 4I, another exemplary method of producing asemiconductor device is shown generally at 400 and is hereinafterreferred to as “method 400.” In method 400, processing is performed on aback surface of the device before processing is performed on a frontsurface of the device.

As shown in FIG. 4A, a spall-inducing stressor layer stack 410 is formedand deposited onto a substrate comprising a semiconductor material(e.g., a 100-oriented silicon material forming a substrate or anymaterial selected from the group consisting of silicon, germanium, SiGe,bulk III-V materials, any of the foregoing materials further includingepitaxially grown semiconductor layers, any of the foregoing materialsfurther including doped layers, metallic layers, and/or passivatinglayers, and combinations of the foregoing) forming a semiconductor layer430 configured to have an exposed front surface and a back surface thatreceives the stressor layer stack 410. A contact-hole patternedpassivation layer may also be deposited on the semiconductor layer 430,with a blanket conductive layer in contact with the passivation layerand the semiconductor layer 430 exposed by the contact-holes. Thestressor layer stack 410 comprises an adhesion layer 415 of titaniumdeposited on the back surface of the semiconductor layer 430 as well asa seed layer 416 of nickel deposited on the adhesion layer 415,deposition being by, for example, sputtering. A stressor layer 420 ofnickel may be deposited onto the seed layer. An ultraviolet (UV)releasable tape 425 may then be applied to the stressor layer 420.

The semiconductor layer 430 may be separated at a plane 433 extendinglongitudinally through the semiconductor layer 430 parallel to theadhesion layer 415. Separation of the semiconductor layer 430 may resultin the semiconductor layer 430 having reduced thickness T as shown inFIG. 4B.

As shown in FIG. 4C, an interfacial release layer 450 is formed on anexposed surface of the semiconductor layer 430 prior to bonding of thestressor layer stack 410 and the semiconductor layer 430 to the epoxyadhesive 435 on a handle substrate 440. When the semiconductor layer 430comprises a silicon or silicon oxide-containing semiconductor material,the interfacial release layer 450 comprises aluminum. However, whilealuminum on a native silicon oxide-containing semiconductor materialprovides a suitable interfacial release layer 450, other materials(alone or in combination with aluminum) may be used as well. Forexample, carbon or hydrocarbon contamination may be introduced to thesilicon surface prior to the aluminum deposition. Suitable methods fordepositing the aluminum interfacial release layer 450 onto thesemiconductor layer 430 include, but are not limited to, thermalevaporation.

As shown in FIG. 4D, the interfacial release layer 450, along with theattached semiconductor layer 430, is transferred and bonded to the epoxyadhesive 435 on the handle substrate 440 using pressure to substantiallyuniformly distribute the epoxy adhesive 435 on at least a portion of afront surface 442 of the handle substrate 440, thereby facilitating asubstantially bubble-free epoxy adhesive bond between the handlesubstrate 440 and the semiconductor layer 430. The UV releasable tape425 is removed from the stressor layer 420 after epoxy curing.

As shown in FIG. 4E, some or all of the stressor layer stack 410 isremoved from the semiconductor layer 430 (for example, by an etchingprocess or an acid wash). Processing steps (e.g., patterning, thermaltreatments (such as heating, if necessary), film depositions, thinningand etching of semiconductor layer 430, and the like) are then performedon the semiconductor layer 430 as well as on any layers thereupon formed(e.g., from the patterning, film depositions) to form a processedsemiconductor layer 430 that is flexible upon release from handlesubstrate 440.

Referring now to FIG. 4F, once some or all of the stressor layer stack410 is removed from the semiconductor layer 430, the processing on theback surface may comprise application of a back surface field (BSF)layer (hereinafter “BSF 485”) to the semiconductor layer 430. The BSF485 may comprise localized BSF regions or contact regions 490 and backreflector elements 495. The BSF 485 may be a low-temperature BSFcomprised of low-temperature deposited. (less than about 450° C.)silicon dioxide back-reflector elements 495 with an array of openingsfilled with evaporated or sputtered metal contact regions 490. Part ofthe back surface field could be formed in the surface of semiconductorlayer 430 prior to the separation step depicted in FIGS. 4A and 4B. Forexample, Al may be evaporated and diffused into the surface of handlesubstrate 430 (FIG. 4A) prior to depositing a Ti adhesion layer 415 toform a back surface field before separation.

As shown in FIGS. 4G and 4H, optional processing can be provided toinclude cell isolation. In various exemplary embodiments of isolatingcells in the flexible semiconductor layer 430, a blanket layer ofhardmask 470 may be deposited on the BSF 485 and patterned and etchedthrough a photoresist (PR) mask or a shadow mask, and/or laser scribingmay be used. A contiguous region of the semiconductor layer 430 may beidentified, such a region including a majority of the surface of thesemiconductor layer. The processing may include the forming of a cellfront structure on the region defined by the majority of the surface.

As shown in FIG. 4I, a conductive, flexible pressure-sensitive carriertape 460 (which may be conductive) may be disposed on the hardmask 470and used to remove a portion of the flexible semiconductor layer 430from the interfacial release layer 450 (and the underlying epoxyadhesive 435 and the handle substrate 440). The flexible semiconductorlayer 430 on the flexible pressure-sensitive carrier tape 460 mayinclude a cell back structure between the flexible pressure-sensitivecarrier tape 460 and the flexible semiconductor layer 430. Cell frontprocessing may then be completed (if desired) with the semiconductor onthe flexible pressure-sensitive carrier tape 460.

As shown in FIGS. 5A through 5L, another exemplary method of producing asemiconductor device is shown generally at 500 and is hereinafterreferred to as “method 500.” In method 500, variations of providingflexible semiconductor devices in which fronts of the semiconductordevices are processed before backs of the semiconductor devices areprocessed are shown. The front processing may be performed before thebacking layer application and removal or after the backing layer removal(as shown in FIGS. 5A through 5L). The back processing may be performed(if desired) with the semiconductor device on a carrier tape. Asemiconductor device fabricated by the method 500 allows for some devicetesting prior to transfer of the semiconductor device to the carriertape.

As shown in FIG. 5A, a spall-inducing stressor layer stack 510 is formedand deposited onto a substrate comprising a semiconductor material(e.g., a. 100-oriented silicon material forming a substrate or anymaterial selected from the group consisting of silicon, germanium, SiGe,bulk III-V materials, any of the foregoing materials further includingepitaxially grown semiconductor layers, any of the foregoing materialsfurther including doped layers, metallic layers, and/or passivatinglayers, and combinations of the foregoing) forming a semiconductor layer530 configured to have an exposed front surface and a back surface thatreceives the stressor layer stack 510. A contact-hole patternedpassivation layer may also be deposited on the semiconductor layer 530,with a blanket conductive layer in contact with the passivation layerand the semiconductor layer 530 exposed by the contact-holes. Thestressor layer stack 510 comprises an adhesion layer 515 of titaniumdeposited on the back surface of the semiconductor layer 530 as well asa seed layer 516 of nickel deposited on the adhesion layer 515,deposition being by, for example, sputtering. A stressor layer 520 ofnickel may be deposited onto the seed layer. An ultraviolet (UV)releasable tape 525 may then be applied to the stressor layer 520.

The semiconductor layer 530 may be separated at a plane 533 extendinglongitudinally through the semiconductor layer 530 parallel to theadhesion layer 515. Separation of the semiconductor layer 530 may resultin the configuration of the stressor layer stack 510 having thesemiconductor layer 530 of reduced thickness T as shown in FIG. 5B.

As shown in FIG. 5C, an interfacial release layer 550 is formed on anexposed surface of the semiconductor layer 530 prior to bonding of thestressor layer stack 510 and the semiconductor layer 530 to the epoxyadhesive 535 on a handle substrate 540. When the semiconductor layer 530comprises a silicon or silicon oxide-containing semiconductor material,the interfacial release layer 550 comprises aluminum. However, whilealuminum on a native silicon oxide-containing semiconductor materialprovides a suitable interfacial release layer 550, other materials(alone or in combination with aluminum) may be used as well. Forexample, carbon or hydrocarbon contamination may be introduced to thesilicon surface prior to the aluminum deposition. Suitable methods fordepositing the aluminum interfacial release layer 550 onto thesemiconductor layer 530 include, but are not limited to, thermalevaporation.

As shown in FIG. 5D, the interfacial release layer 550, along with theattached semiconductor layer 530, is transferred and bonded to the epoxyadhesive 535 on the handle substrate 540 using pressure to substantiallyuniformly distribute the epoxy adhesive on at least a portion of thefront surface 542 of the handle substrate 540, thereby facilitating asubstantially bubble-free epoxy adhesive bond between the handlesubstrate 540 and the semiconductor layer 530. The UV releasable tape525 is removed from the stressor layer 520 after the epoxy curing step.

As shown in FIG. 5E, some or all of the stressor layer stack 510 isremoved from the semiconductor layer 530 (for example, by an etchingprocess or an acid wash). Processing steps (e.g., patterning, thermaltreatments (such as heating, if necessary), film depositions, and thelike) are then performed on the semiconductor layer 530 as well as onany layers thereupon formed (e.g., from the patterning, filmdepositions) to form a processed semiconductor layer 530 that isflexible upon release from handle substrate 540.

Referring now to FIG. 5F, a layer 580 comprising a finger/bus metal 582and an anti-reflective coating (ARC) 584 is deposited on the flexiblesemiconductor layer 530. Methods by which the finger/bus metal 582 isdeposited include, but are not limited to, evaporation, sputtering,electroplating, or combinations thereof. Materials typically used forthe finger/bus metal include, but are not limited to, Ti, Ni, Pd, Au,Ni, Cu, Ge, Al, Ag, and combinations thereof. Methods by which theanti-reflective coating (ARC) 584 is deposited include evaporation,sputtering, atomic layer deposition (ALD), or other chemical vapordeposition (CVD) based processes. Typical materials used for ARC 584include, but are not limited to, oxides and nitrides of semiconductorsand metals (e.g., silicon oxide or nitride, aluminum oxide, magnesiumoxide, etc.) and combinations thereof.

Referring now to FIGS. 5G and 5H, a sacrificial mask 586 is deposited ona portion of the layer 580 comprising the finger/bus metal 582, and anetching process may be used to remove portions of the layer 580, theflexible semiconductor layer 530, and the interfacial release layer 550down to the epoxy adhesive 535 to pattern the layer 580. The etchingprocess used may comprise wet or dry etching to isolate the cell definedby the sacrificial mask 586.

Referring now to FIG. 5I, the sacrificial mask 586 is removed using anysuitable etching process.

Referring now to FIGS. 5J and 5K, a tape superstrate 588 is deposited onthe remaining exposed layer 580, and the flexible semiconductor layer530 is removed from the interfacial release layer 550. As shown in FIG.5K, the tape superstrate 588 may include a metal portion to provide acontact 590 to the finger/bus metal 582 of the layer 580. Use of thetape superstrate 588 is particularly useful when the tape superstrate588 is transparent and compatible with the front contact (e.g., when thetape superstrate 588 includes contact holes).

Referring now to FIG. 5L, the tape superstrate 588 is removed, thecontact 590 remains on the layer 580.

Referring now to FIG. 6, a simplified block diagram of variouselectronic devices and apparatus that are suitable for use in practicingthe exemplary embodiments described herein is shown. For example, acomputer 610 may be used to control one or more of the fabricationprocesses as described above. The computer 610 includes a controller,such as a computer or a data processor (DP) 614 and a computer-readablememory medium embodied as a memory (MEM) 616 that stores a program ofcomputer instructions (PROG) 618.

The PROG 618 includes program instructions that, when executed by theassociated DP 614, enable the various electronic devices and apparatusto operate in accordance with exemplary embodiments. That is, variousexemplary embodiments may be implemented at least in part by computersoftware executable by the DP 614 of the computer 610, or by hardware,or by a combination of software and hardware (and firmware).

The computer 610 may also include dedicated processors, for exampleflexible semiconductor modeling processor 615.

The computer readable MEM 616 may be of any type suitable to the localtechnical environment and may be implemented using any suitable datastorage technology, such as semiconductor based memory devices, flashmemory, magnetic memory devices and systems, optical memory devices andsystems, fixed memory, and removable memory. The DP 614 may be of anytype suitable to the local technical environment, and may include one ormore of general purpose computers, special purpose computers,microprocessors, digital signal processors (DSPs), and processors basedon a multicore processor architecture, as non-limiting examples.

The exemplary embodiments, as discussed herein and as particularlydescribed with respect to exemplary methods, may be implemented inconjunction with a program storage device (e.g., at least one memory)readable by a machine, tangibly embodying a program of instructions(e.g., a program or computer program) executable by the machine forperforming operations. The operations comprise utilizing the exemplaryembodiments of the method.

Based on the foregoing it should be apparent that various exemplaryembodiments provide a method to fabricate flexible semiconductor layersand devices on flexible carriers.

FIG. 7 is a logic flow diagram that illustrates the operation of amethod 700 (and a result of an execution of computer programinstructions (such as PROG 618)), in accordance with the exemplaryembodiments. In accordance with these exemplary embodiments, a stressorlayer stack is formed on a first surface of a semiconductor substrate atblock 710. An interfacial release layer is subsequently formed on anexposed second surface of the semiconductor substrate at block 720. Atblock 730, the interfacial release layer is then adhesively bonded to arigid handle substrate using an epoxy. At least a portion of thestressor layer stack is removed from the first surface of thesemiconductor substrate at block 740. At block 750, the semiconductorsubstrate is then processed to impart flexibility to the semiconductorsubstrate. At block 760, the semiconductor substrate is then removedfrom the interfacial release layer.

The various blocks of method 700 shown in FIG. 7 may be viewed as methodsteps, and/or as operations that result from operation of computerprogram code, and/or as a plurality of coupled logic circuit elementsconstructed to carry out the associated function(s).

EXAMPLE

In one example of a method of using an interfacial release layer asdescribed in FIGS. 2A through 2E, the stressor layer stack 210 wasdeposited on a 100-oriented silicon (Si) substrate (semiconductor layer230) to form a silicon film. The stressor layer stack 210 included theadhesion layer 215 of titanium (Ti) (150 nanometers (nm) in thickness)and the seed layer of nickel (Ni) (400 nm in thickness), both depositedby sputtering, and the stressor layer 220 of electroplated Ni (5micrometers (μm) in thickness) on top of the seed layer of Ni. The Niwas electroplated on a 2 inch diameter area of the Si substrate. The UVreleasable tape 225 was then applied to the stressor layer 220 to inducethe spalling.

After the Si film was spalled, a 300 nm aluminum (Al) layer wasthermally evaporated on the spalled Si surface without removing thenative oxide formed on the Si film after spalling, the Al layer formingthe interfacial release layer 250. The Al side of the resulting flexiblefilm assembly (tape/stressor layer/Si/Al), which formed the interfacialrelease layer 250, was bonded with the epoxy adhesive 235 to the handlesubstrate 240, which had been coated with 300 nm of thermally evaporatedAl. This metal layer exhibited suitable adhesion with the epoxy adhesive235. The epoxy adhesive 235 used was an electrically conductivesilver-filled epoxy (Ablebond 2030SC®, which is available from HenkelNorth America). A pressure was applied during the curing process byapplying a weight on the top of the sample. The curing temperature was80 degrees C., with a curing time of 1 hour 15 minutes.

After the curing process was finished, the UV releasable tape 225 wasthen removed by exposure to UV light. The Ni stressor layer 220 and theTi adhesion layer 215 were removed with selective chemical etchants.Using the UV releasable tape 225 as a flexible substrate, the siliconfilm was released from the interfacial release layer 250. This waspossible because the adhesion of Al in the interfacial release layer 250to the spalled silicon film is weaker than the adhesion of Al in theinterfacial release layer 250 to the epoxy. It was speculated that theweak Al to Si adhesion was a result of surface contaminants present onthe untreated silicon film surface prior to Al thermal evaporation.Different photos of the sample corresponding to the steps of FIGS. 2C,2D, and 2E are shown in FIGS. 8A through 8D.

Referring now to FIGS. 8A through 8D, images of the silicon filmtransfer at various stages of method 200 are shown. In FIG. 8A, a topview image of the nickel seed layer (corresponding to FIG. 2C) is shown.In FIG. 8B, a top view image of the semiconductor layer 230 with the Niseed layer and the Ti adhesion layer 215 removed (corresponding to FIG.2D) is shown. In FIG. 8C, a top view image of the flexible semiconductorlayer 230 (e.g., showing the silicon of the 100-oriented siliconsubstrate) with the pressure-sensitive carrier tape 260 down(corresponding to the upper portion of FIG. 2E) is shown. In FIG. 8D,the interfacial release layer 250 from which the flexible semiconductorlayer 230 is removed (corresponding to the lower portion of FIG. 2E) isshown.

In one example embodiment, a method for fabricating a semiconductordevice comprises providing a preformed spalled structure comprising astressor layer stack on a first surface of a semiconductor substrate;forming an interfacial release layer on an exposed second surface of thesemiconductor substrate; adhesively bonding the interfacial releaselayer to a rigid handle substrate using an epoxy; removing at least aportion of the stressor layer stack from the first surface of thesemiconductor substrate; processing the semiconductor substrate; andremoving the semiconductor substrate from the interfacial release layerto impart flexibility to the semiconductor substrate.

Forming a stressor layer stack on a first surface of a semiconductorsubstrate may comprise depositing an adhesion layer on the semiconductorsubstrate, depositing a seed layer on the adhesion layer, depositing astressor layer on the seed layer, and applying a releasable tape to thestressor layer. Forming an interfacial release layer on an exposedsecond surface of the semiconductor substrate may comprise thermallyevaporating an aluminum-containing compound on the semiconductorsubstrate. The method may further comprise introducing a contaminant toa surface of the semiconductor substrate prior to thermally evaporatingan aluminum-containing compound on the semiconductor substrate. Removingthe semiconductor substrate from the interfacial release layer maycomprise separating the semiconductor substrate from the interfacialrelease layer using a pressure-sensitive carrier tape. Processing thesemiconductor substrate prior to removing the semiconductor substratefrom the interfacial release layer may comprise one or more ofpatterning the semiconductor substrate, thermally treating thesemiconductor substrate, and depositing a film on the semiconductorsubstrate. The method may further comprise separating the semiconductorsubstrate along a plane extending longitudinally through thesemiconductor substrate parallel to the interfacial release layer toreduce a thickness of the semiconductor substrate. The method mayfurther comprise isolating cells in the semiconductor substrate.Isolating cells in the semiconductor substrate may comprise applying ahardmask to the semiconductor substrate and etching exposedsemiconductor substrate down to the epoxy. The method may furthercomprise applying a pressure-sensitive tape to the hardmask to removethe semiconductor substrate from the interfacial release layer. Themethod may still further comprise removing the hardmask and applying apressure-sensitive tape to the hardmask to remove the semiconductorsubstrate from the interfacial release layer.

In another example embodiment, a method for fabricating a semiconductordevice comprises providing a preformed spalled structure comprising astressor layer stack on a first surface of a semiconductor substrate;forming an interfacial release layer on a second exposed surface of thesemiconductor substrate; bonding the interfacial release layer to arigid handle substrate using an epoxy adhesive; removing at least aportion of the stressor layer stack from the semiconductor substrate;processing the semiconductor substrate; applying a back surface fieldlayer to the semiconductor layer; isolating cells in the back contactlayer and the semiconductor substrate; and removing the semiconductorsubstrate from the interfacial release layer using a pressure-sensitivecarrier tape to impart flexibility.

Isolating cells in the back contact layer and the semiconductorsubstrate may comprise patterning the back contact layer and etching theback contact layer and semiconductor substrate down to the epoxyadhesive. Patterning the back contact layer may comprise applying ahardmask to the back contact layer. Etching the back contact layer andsemiconductor substrate may comprise one or more of etching through aphotoresist mask, etching through a shadow mask, and laser scribing.

In another example embodiment, a method for fabricating a semiconductordevice comprises providing a preformed spalled structure comprising astressor layer stack on a first surface of a semiconductor substrate;forming an interfacial release layer on a second exposed surface of thesemiconductor substrate; bonding the interfacial release layer to arigid handle substrate using an epoxy adhesive; removing at least aportion of the stressor layer stack from the semiconductor substrate;processing the semiconductor substrate; forming a layer comprising afinger/bus metal and an anti-reflective coating on the semiconductorsubstrate; applying a sacrificial mask to the layer comprising thefinger/bus metal and the anti-reflective coating; patterning the layercomprising the finger/bus metal and the anti-reflective coating;removing the sacrificial mask; and removing the semiconductor substratefrom the interfacial release layer using a tape superstrate to impartflexibility.

Processing the semiconductor substrate may comprise one or more ofpatterning the semiconductor substrate, thermally treating thesemiconductor substrate, and depositing a film on the semiconductorsubstrate. The method may further comprise etching portions of the layercomprising the finger/bus metal and the anti-reflective coating down tothe epoxy adhesive. The method may further comprise providing a metalportion in the tape superstrate to provide a contact to the finger/busmetal.

In the foregoing description, numerous specific details are set forth,such as particular structures, components, materials, dimensions,processing steps, and techniques, in order to provide a thoroughunderstanding of the exemplary embodiments disclosed herein. However, itwill be appreciated by one of ordinary skill of the art that theexemplary embodiments disclosed herein may be practiced without thesespecific details. Additionally, details of well-known structures orprocessing steps may have been omitted or may have not been described inorder to avoid obscuring the presented embodiments. It will beunderstood that when an element as a layer, region, or substrate isreferred to as being “on” or “over” another element, it can be directlyon the other element or intervening elements may also be present. Incontrast, when an element is referred to as being “directly on” or“directly” over another element, there are no intervening elementspresent. It will also be understood that when an element is referred toas being “beneath” or “under” another element, it can be directlybeneath or under the other element, or intervening elements may bepresent. In contrast, when an element is referred to as being “directlybeneath” or “directly under” another element, there are no, interveningelements present.

The description of the present invention has been presented for purposesof illustration and description, but is not intended to be exhaustive orlimiting in the form disclosed. Many modifications and variations willbe apparent to those of ordinary skill in the art without departing fromthe scope of the invention. The embodiments were chosen and described inorder to best explain the principles of the invention and the practicalapplications, and to enable others of ordinary skill in the art tounderstand the invention for various embodiments with variousmodifications as are suited to the particular uses contemplated.

What is claimed is:
 1. A method for fabricating a semiconductor device,comprising: providing a structure comprising a stressor layer stack on afirst surface of a semiconductor substrate; forming an interfacialrelease layer on a second exposed surface of the semiconductorsubstrate; bonding the interfacial release layer to a rigid handlesubstrate using an epoxy adhesive; removing at least a portion of thestressor layer stack from the semiconductor substrate; processing thesemiconductor substrate; forming a layer comprising a finger/bus metaland an anti-reflective coating on the semiconductor substrate; applyinga sacrificial mask to the layer comprising the finger/bus metal and theanti-reflective coating; patterning the layer comprising the finger/busmetal and the anti-reflective coating; removing the sacrificial mask;and removing the semiconductor substrate from the interfacial releaselayer using a tape superstrate to impart flexibility to thesemiconductor substrate.
 2. The method of claim 1, wherein processingthe semiconductor substrate comprises one or more of patterning thesemiconductor substrate, thinning the semiconductor substrate, thermallytreating the semiconductor substrate, and depositing a film on thesemiconductor substrate.
 3. The method of claim 1, further comprisingetching portions of the layer comprising the finger/bus metal and theanti-reflective coating down to the epoxy adhesive.
 4. The method ofclaim 1, further comprising providing a metal portion in the tapesuperstrate to provide a contact to the finger/bus metal.
 5. The methodof claim 1, further comprising separating the semiconductor substratealong a plane extending longitudinally through the semiconductorsubstrate parallel to the first surface of the semiconductor substrateto reduce a thickness of the semiconductor substrate and expose a secondsurface of the semiconductor substrate.
 6. The method of claim 5,wherein separating the semiconductor substrate along a plane extendinglongitudinally through the semiconductor substrate comprisesmechanically guiding at least a portion of the stressor layer stack toinduce and sustain a spalling mode fracture.
 7. The method of claim 1,wherein providing a structure comprising a stressor layer stackcomprises forming an adhesion layer on the semiconductor substrate,forming a seed layer on the adhesion layer, forming a stressor layer onthe seed layer, and applying a releasable tape to the stressor layerstack.
 8. The method of claim 7, further comprising depositing a layerof titanium on the semiconductor substrate by sputtering to form theadhesion layer, depositing a layer of nickel on the adhesion layer bysputtering to form the seed layer, and depositing a layer of nickel onthe seed layer by sputtering to form the stressor layer.
 9. The methodof claim 1, wherein the finger/bus metal is selected from the group ofmetals consisting of Ti, Ni, Pd, Au, Ni, Cu, Ge, Al, Ag, andcombinations of the foregoing materials.
 10. The method of claim 1,wherein the anti-reflective coating is a material selected from thegroup consisting of oxides of semiconductors, nitrides ofsemiconductors, oxides of metals, nitrides of metals, and combinationsof the foregoing materials.
 11. The method of claim 1, wherein thesemiconductor substrate comprises 100-oriented silicon material.
 12. Themethod of claim 1, wherein the semiconductor substrate is a materialselected from the group consisting of silicon, germanium, SiGe, bulkIII-V materials, any of the foregoing materials further includingepitaxially grown semiconductor layers, any of the foregoing materialsfurther including doped layers, metallic layers, and/or passivatinglayers, and combinations of the foregoing materials.
 13. The method ofclaim 1, wherein the semiconductor substrate comprises a silicon orsilicon-containing semiconductor material and the interfacial releaselayer comprises aluminum.